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Pollens
Thu Apr 22, 2004
Listen in RealAudio 
Do you dread the coming of spring with those puffy eyes and runny nose? It's those
danged windborne pollens. Hi, I'm Bryan Yeaton for The Weather Notebook.
For many Americans, certain plant pollens cause allergic reactions when they enter the
eyes and nose. Although any pollen can cause such reactions, the prime culprits are
the windblown pollens, extremely light pollens designed to be dispersed by the wind.
Trees, grasses, and certain weeds broadcast them in immense quantities, for
windblown pollination is a true hit-or-miss procedure. In contrast, colourful, fragrant
flowers produce much heavier pollens that don't easily become airborne, and use
insects for dispersal.
Allergists commonly divide spring pollen season into early and late spring depending
on the region and vegetation mix. Early spring allergies begin in March or April, driven
by pollens from about 65 common tree species. Twenty grass species, including
Bermuda and Kentucky bluegrass, produce their pollens starting in late
spring.
Obviously, wind plays a major role in the release and spread of airborne pollen, but
other factors, including temperature and precipitation, contribute as well. Warm, dry,
breezy days provide optimal weather for large pollen releases.
Pollens released from grasses usually only rise high into the air during daylight hours.
Tree pollens, in contrast, waft away any time the wind blows strong enough to dislodge
them. Once airborne, pollens can travel hundreds of miles.
Early morning hours are often the worst time for sufferers because pollens accumulate
in the stable surface air. High pollen counts often persist through the night and may
increase in the evening when winds and vertical mixing decrease, and pollen aloft
settles into the now-still surface air.
Thanks to our contributing writer, meteorologist Keith Heidorn. The Weather Notebook
comes to you through the generous support of Subaru of America and the National
Science Foundation.
Today's Links
Aeroallergens: Misery Blowin\' In The Wind
http://www.islandnet.com/~see/weather/almanac/arc2001/alm01aug.htm
Aerobiology Research Laboratories: Pollen Allergen
http://www.pollenplus.com/pollen/index.html
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